Rear wheel steering arrangement

ABSTRACT

A rear wheel steering arrangement for a motor vehicle having a pair of rear wheels connected to the vehicle by forward and rearward transverse suspension arms comprises a body member extending transversely between each of the rear wheels, the slide member mounted on the body member and being connected to an inboard end of each of the rearward suspension arms, and a steering mechanism having an input shaft and an output shaft. The output shaft is connected to the slide member and the steering mechanism drives the slide member axially along the transvrese member causing the rearward suspension arms to move in common with the slide member so as to produce a steering action on the rear wheels.

BACKGROUND OF THE INVENTION

This invention relates to a rear wheel steering arrangement for a motorvehicle, and in particular to a steering arrangement where all fourwheels of the car are steered.

Various designs of four wheel steering systems are known. In suchsystems, the front wheels are always the fundamental steeringcomponents, and turning of the front wheels is the major controllingfactor on the steering of the vehicle. The rear wheels are steered to alesser degree; at low speeds to assist in parking and manoeuvring and athigh speeds to improve handling and stability of the vehicle. At lowspeeds it is conventional to turn the rear wheels in the same directionas the front wheels whilst at high speeds it is conventional to turn therear wheels in the opposite sense to the front wheels.

These different requirements are accomplished in various different waysby known four wheel steering systems, but it is normally the case thatthe rear wheel suspension/drive/steering arrangement requiresconsiderable modification as compared with a conventional vehicle withnon-steered rear wheels. This leads to added complexity and cost, andmay compromise the suspension layout.

SUMMARY OF THE INVENTION

According to the invention there is provided a rear wheel steeringarrangement for a motor vehicle, the arrangement including a pair ofrear wheels which are each connected to the vehicle by a forward and bya rearward transverse suspension arm, and a steering mechanism which hasan input and an output, characterised in that the output of the steeringmechanism is connected to a common actuator mounted on the vehicle sothat movement of the steering mechanism output produces movement of theactuator on either side of :he vehicle centreline, the inboard ends oftwo of the suspension arms, one on each side of the vehicle, beingconnected to the actuator so that they are moved transversely in commonby the common actuator to produce a steering action on the rear wheels.

This arrangement allows the inboard ends of the suspension/steering armsto be kept close to the centre line of the vehicle and this hassignificant advantages for the suspension geometry of the steeredwheels. Because one set of arms is able to act both as suspension and assteering links and no dedicated steering links are required,considerable complexity reductions can be made.

In one form of the invention, the inboard ends of the suspension armsmay be connected to the common actuator which is pivoted at a fixedpoint on the centreline of the vehicle.

The fact that the actuator is pivoted on a fixed part of the vehicle (oron a chassis sub-frame) has the result that the pivot bearing supports asubstantial part of the load which would otherwise be carried directlyby the steering mechanism output.

The steering mechanism may be a conventional end take-off steering gearwith the take-off shaft being mounted to one or other side of thevehicle centreline and connected to the common actuator through atransfer linkage.

The common actuator may be pivotally mounted on the steering mechanismhousing, the housing itself being rigidly mounted to the vehicle body.

The transfer linkage preferably takes the form of a hinged link which ishinged at one end to an arm mounted on the steering mechanism take-offshaft and-at the other end to the common actuator.

The steering arms may be connected to the actuator through flexiblejoints which preferably incorporate rubber bushes.

In another form of the invention, the common actuator is in the form ofa slide member which is slidably mounted on a transversely extendingbody member of the vehicle between the rear wheels, the steeringmechanism is arranged to drive the slide member to and fro along thetransverse member, and the suspension/steering arms are connected to theslide member so that a steering action is produced as the slide membermoves along the transverse member.

The steering mechanism can be a motor (electrical or hydraulic) which iscontrolled by a control unit which determines the desired steering angleof the rear wheels in accordance with various parameters fed to theunit.

The steering mechanism is preferably connected to the slide memberthrough a linkage which is constructed so that forces acting on theslide member do not cause the motor to be driven.

The slide member is preferably in the form of a saddle which slides on atransverse chassis member. The suspension arms can be connected to thesaddle by means of bolts which pass through elongate slots in thechassis member, the elongate slots being arranged so that a limitedamount of longitudinal movement is permitted but also so that the saddleis permanently connected to the chassis member.

Such an arrangement has the advantage that it can be constructed using alarge number of existing parts and without radical changes to the rearwheel suspension layout. Even if the steering action on the rear wheelsis only through a limited angle, this is quite adequate to provide thebenefits of rear wheel steering at speeds above manoeuvring speeds.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a plan view of a rear wheel steering arrangement in accordancewith a first embodiment of the invention;

FIG. 2 is a side view of the steering arrangement;

FIG. 3 is an elevation of the arrangement, as seen from the rear of thevehicle;

FIG. 4 shows a general arrangement of a back axle with a secondembodiment of steering arrangement in accordance with the invention;

FIG. 5 shows certain components of the arrangement of FIG. 4;

FIG. 6 is a cross section through the saddle and chassis member of FIG.5;

FIG. 7 is a detailed view of part of the assembly shown in FIG. 6;

FIG. 8 is a cross-section corresponding to the section of FIG. 6 butshowing an alternative bearing arrangement; and

FIG. 9 is an exploded perspective view of the saddle and chassis memberin another alternative arrangement, viewed from above.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, the centreline of the vehicle is indicated by a chain-dottedline 10, and a rear wheel as shown at 12. The rear wheel is mounted on awheel knuckle 14 supported by suspension links 16, 18 and 20. The wheel12 is a non-driven but steered wheel, and the link 20 also acts as asteering arm 20 connected to the knuckle 14 to transmit steeringmovement. FIG. 1 shows only one side of the vehicle, and the arrangementshown in FIG. 1 will be repeated substantially symmetrically on theother side of the centreline 10.

In the middle of the vehicle a steering mechanism 22 is mounted and thishas an input shaft 24 from the steering wheel at the front of thevehicle. The mechanism 22 also has an output shaft 26.

The steering mechanism is based on a conventional end take-off steeringgear as used for conventional front wheel steering systems. To adapt thegear for the rear wheel steering system described here, there may be anarrangement within the housing 22 which converts movement of the inputshaft 24 to a movement of the output shaft 26 in accordance with anysuitable system for rear wheel steering. For example, the wheels mayturn in the opposite sense to the front wheels at low steering angles(which are assumed to occur at high vehicle speeds) and may turn in thesame sense at greater steering angles as needed for low speedmanoeuvring. Gear arrangements to accomplish this result are inthemselves known and form no part of this invention.

Alternatively the adaptation to a rear wheel steering set-up may becarried out by for example an electronically controlled device (notshown) which controls the movement of the output shaft 26.

The suspension links 20, 20a are both pivoted on a common actuator 28which is secured to the housing 22 at a pivot point 30, and hangs fromthat pivot point. At the bottom of the actuator, a hinged link 32connects the actuator to an arm 34 fixed to the output shaft 26. As theoutput shaft moves linearly, the arm 34 moves with it and the hingedlink 32 then causes the actuator 28 to turn in one or other directionabout its axis 30. This causes the suspension links 20, 20a to be movedso that the wheel knuckles 14 are turned about the steering axis 34 toeffect a steering action.

The connections between the ends of the link 32, the arm 34 and theactuator 28 respectively may all be accomplished through rubber bushedjoints which accommodate the relative twisting movement required as aresult of the system geometry.

As a result of the fact that the steering arm actuator 28 is mounted onthe centreline of the vehicle, the links 20, 20a themselves have amaximum length. This is of great advantage in achieving a suitablesuspension geometry for the rear, steered wheels. Furthermore asubstantial proportion of the reaction loads imposed on the steeringmechanism when the wheels are being steered is supported through thepivot point 30, rather than being transmitted directly to the outputshaft 26 of the mechanism.

FIG. 4 shows a typical rear wheel arrangement with road wheels 110, 112supported on suspension struts 114, 116 and linked to a sub frame 118through suspension links 120, 122, 124, 126. The links 124, 126 also actas steering arms. Longitudinal locating links are provided of which onlyone is shown in the Figure at 128.

The sub frame 118 is of a substantially conventional construction andhas a rear region 130 in the form of a transverse rail.

A saddle 132 fits over the rail and is retained and guided on the railthrough a slot 133 on the top face of the saddle which engages with aT-shaped web 134 on the rail. The ends of the suspension links 124, 126are connected to the saddle in the manner shown in FIG. 3, where a bolt136 passes through the end of the link 124 and is secured at the twosides of the saddle 132. In FIG. 6 of the drawings, thesteering/suspension link 124 is supported centrally in the saddle by twobushings 138, 140, and these bushings together with the bolt 136 passthrough elongate slots 142 in the side wall of the rail part 130 of thesub frame 118.

A motor 144 is located close to the saddle 132 and will be secured to aconvenient part of the suspension sub-frame or of the vehicle body.Mounting the motor on the sub-frame has considerable advantages in thatit enables the sub-frame to become a complete sub-assembly, thusremoving any tolerance problems on assembly. The motor may beelectrically driven or hydraulically driven and will be caused tooperate by receiving a control signal from a control unit which itselfreceives operating signals from appropriate other parts of the vehicle.The motor 144 shown in the drawings drives a gear contained within ahousing 146 which produces a rotating output on a shaft 148. This causesa crank 150 to move a link arm 152 backwards and forwards, and the linkarm 152 is connected directly to the saddle 132. In fact only a verysmall amount of movement is necessary to produce an effective rear wheelsteering action when the vehicle is at speed. All that is needed underthese conditions is up to two degrees of steering movement of thewheels, and this can be achieved by allowing the saddle 132 to movetypically ±5 mm from a centre position.

The construction shown in FIGS. 4 to 7 shows the saddle 132 guided onthe chassis member 130 by the location of the bushes 138 in the slots142. This type of guiding may be adequate for very small steeringangles, but a full slide guide mechanism can be used to allow greatersteering angles to be used.

FIG. 8 shows a construction where the saddle 232 has upper guide shoes238 which run on needle bearings 240 mounted on the V-shaped guide edgesof the web 234. A bolt 236 which supports the suspension/steering link224 is a clearance fit in slots 242 in the chassis member 230.

In FIG. 9, the web 334 carries axially extending guide rods 335 (whichare shown foreshortened in the drawing), and guide shoes 338 are mountedon the top of the saddle with bearing bores 337 through them to receivethe rods 335. In other respects, the embodiments of FIGS. 8 and 9 havefeatures similar to the embodiments described earlier.

The construction of the motor and the mechanism through which the motordrive is transferred to the saddle will be arranged so that forcesacting up the links through the saddle to the motor do not causerotation of the motor. By suitably arranging this mechanism, such as inthe form of a worm drive, the size of the motor and hence its powerconsumption can be minimised.

With the arrangement shown, it is possible to use the same basicsuspension geometry for both two wheel steering and four wheel steeringderivatives of the same basic vehicle as the links, bushings and lineassembly procedures can be the same for both.

We claim:
 1. A rear wheel steering arrangement for a motor vehiclehaving a pair of rear wheels each connected to the vehicle by a forwardand a rearward transverse suspension arm, the arrangement comprising:abody member extending transversely between each of said rear wheels; aslide member mounted on said transversely extending body member andbeing connected to an inboard end of each of said rearward suspensionarms; and a steering mechanism having an input shaft and an outputshaft, said output shaft being connected to said slide member, saidsteering mechanism being operative to drive said slide member axiallyalong said transverse member about a centerline of the vehicle, causingsaid rearward suspension arms to move in common with said slide memberso as to produce a steering action on said rear wheels.
 2. A rear wheelsteering arrangement as claimed in claim 1, wherein said steeringmechanism includes a take-off shaft being mounted to one or other sideof the vehicle centerline and connected to the slide member through atransfer linkage.
 3. A rear wheel steering arrangement as claimed inclaim 2, wherein the transfer linkage takes the form of a hinged linkwhich is hinged at one end to an arm mounted on the steering mechanismtake-off shaft and at the other end to the slide member.
 4. A rear wheelsteering arrangement as claimed in claim 2 wherein the suspension armswhich are connected to the steering mechanism are connected to the slidemember through flexible joints which incorporate rubber bushes.
 5. Arear wheel steering arrangement as claimed in claim 1 wherein thesteering mechanism is a motor which is controlled by a control unitwhich determines the desired steering angle of the rear wheels inaccordance with various parameters fed to the unit.
 6. A rear wheelsteering arrangement as claimed in claim 5, wherein said motor is anelectrical motor.
 7. A rear wheel steering arrangement as claimed inclaim 5, wherein said motor is hydraulically operated.
 8. A rear wheelsteering arrangement as claimed in claim 1 wherein the steeringmechanism is connected to the slide member through a linkage which isconstructed so that forces acting on the slide member do not cause themotor to be driven.
 9. A rear wheel steering arrangement as claimed inclaim 1 wherein the slide member is in the form of a saddle which slideson a transverse chassis member.
 10. A rear wheel steering arrangement asclaimed in claim 9, wherein the suspension arms are connected to thesaddle by means of blots which pass through elongate slots in thechassis member, the elongate slots being arranged so that a limitedamount of longitudinal movement is permitted but also so that the saddleis permanently connected to the chassis member.
 11. A rear wheelsteering arrangement as claimed in claim 9, wherein said transverselyextending body member includes a T-shaped web projecting therefrom, saidweb being operative to engage a slot disposed in said saddle.
 12. A rearwheel steering arrangement as claimed in claim 1, wherein said saddleincludes a pair of upper guide shoes secured thereto, said guide shoesbeing operative to engage said web.
 13. A rear wheel steeringarrangement as claimed in claim 11, wherein said saddle includes a pairof upper guide shoes secured thereto, said guide shoes including bearingbores therethrough which receive axially extending rods connected tosaid web, so that said saddle is operative to reciprocate axially alongsaid rods.